WO2014081784A1

WO2014081784A1 - Heated ribbon erbium doped fiber

Info

Publication number: WO2014081784A1
Application number: PCT/US2013/070934
Authority: WO
Inventors: Lan Peter MCCLEAN; Peter G. Wigley
Original assignee: II VI Inc
Current assignee: Coherent Corp
Priority date: 2012-11-26
Filing date: 2013-11-20
Publication date: 2014-05-30
Anticipated expiration: 2015-05-26

Abstract

A fiber ribbon cable that includes a plurality of ribbon tubes arranged in a pattern, wherein one of the ribbon tubes contains an optical fiber and an adjacent ribbon tube contains an electric heating element such that when heated the electric heating element is able to adjust the temperature of the optical fiber.

Description

HEATED RIBBON ERBIUM DOPED FIBER

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] This invention relates generally to preventing temperature dependent gain ripple in fiber amplifiers, for example as may be used in reconfigurable optical add-drop multiplexer.

2. Description of the Related Art

[0002] Erbium doped fiber amplifiers (EDFA) used in dense wavelength division multiplexing (DWDM) applications require heating of the Erbium doped fibers to prevent temperature dependent gain ripple. Traditionally, an Erbium doped fiber is heated by, for example, a separate flexible heater element in close contact with the fiber, a heater designed into the PCB, a thermo-electric cooler, or other heating element external to the fiber.

[0003] Reconfigurable optical add-drop multiplexer (ROADM) nodes sometimes are designed to use multiple EDFAs. In these designs, the EDFAs are positioned together on a system card making heating elements for the Erbium fibers difficult to integrate without unduly increasing the size and/or complexity of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

[0005] FIG. 1 A shows a diagram of a first embodiment a fiber ribbon cable arranged in a pattern of a linear array;

[0006] FIG. IB shows a diagram of a second embodiment a fiber ribbon cable arranged in a pattern of a linear array; [0007] FIG. 2A shows a diagram of a first embodiment a fiber ribbon cable arranged in a pattern of a circular array;

[0008] FIG. 2B shows a diagram of a second embodiment a fiber ribbon cable arranged in a pattern of a circular array;

[0009] FIG. 2C shows a diagram of a third embodiment a fiber ribbon cable arranged in a pattern of a circular array;

[0010] FIG. 2D shows a diagram of a fourth embodiment a fiber ribbon cable arranged in a pattern of a circular array; and

[0011] FIG. 3 is a block diagram illustrating an example fiber amplifier.

[0012] For clarity, identical reference numbers have been used, where applicable, to designate identical elements that are common between figures. It is contemplated that features of one embodiment may be incorporated in other embodiments without further recitation. The figures and the following description relate to preferred embodiments by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] FIG. 1A shows a diagram of a first embodiment a fiber ribbon cable 100 arranged in a pattern of a linear array. As shown in exemplary FIG. 1 A, the fiber ribbon cable 100 comprises a plurality of ribbon tubes 105. The ribbon tubes 105 are made out of a material with high thermal conduction. A ribbon tube 105 may contain an optical fiber 115. The optical fiber 115 may be for example, Erbium doped silica. Alternatively, a ribbon tube 105 may contain an electric heating element 110. The electric heating element 110 is used to heat optical fibers to a specific temperature that are in adjacent ribbon tubes 105. The specific temperature value may be set to inhibit temperature dependent gain ripple. For example, the specific temperature value may be 60 degrees Celsius. [0014] Additionally, the fiber ribbon cable 100 is constructed such that each ribbon tube 105 containing an optical fiber is adjacent to a ribbon tube 105 containing the heating element 110. In this embodiment, the optical fiber is the same for the three displayed ribbon tubes containing the optical fiber 115. Meaning that the fiber ribbon cable 100 is constructed such that an optical signal input to the fiber ribbon cable 100 propagates through the optical fiber 115 and also passes through each of the ribbon tubes containing the optical fiber 115 before it exits the fiber ribbon cable 100. The fiber ribbon cable 100 may be used in, for example, a fiber amplifier (e.g., an EDFA). The length of the fiber ribbon cable 100 depends on the amount of desired gain of the fiber amplifier the fiber ribbon cable 100 is implemented in, and the number of ribbon tubes containing the optical fiber 115.

[0015] FIG. IB shows a diagram of a second embodiment a fiber ribbon cable 120 arranged in a pattern of a linear array. The fiber ribbon cable 120 is similar to the fiber ribbon cable 100 described above, however, it has been modified to include three different optical fibers, optical fiber 115, optical fiber 122, and optical fiber 125. One or more of the three different optical fibers may each transport different optical signals from each other. For example, the optical fiber 115, the optical fiber 122, and the optical fiber 125, may transport optical signals A, B, and C, respectively.

[0016] FIG. 2A shows a diagram of a first embodiment a fiber ribbon cable 200 arranged in a pattern of a circular array. As shown in exemplary FIG. 2A, the fiber ribbon cable 200 comprises a plurality of ribbon tubes 105 arranged around a ribbon tube in a center position that contains the heating element 110. The ribbon tubes adjacent to the ribbon tube containing the heating element 110 all contain the same optical fiber 115.

[0017] In this embodiment, the optical fiber is the same for the five displayed ribbon tubes containing the optical fiber 115. Meaning that the fiber ribbon cable 200 is constructed such that an optical signal input to the fiber ribbon cable 200 propagates through the optical fiber 115 and also passes through each of the ribbon tubes containing the optical fiber 115 before it exits the fiber ribbon cable 200. The fiber ribbon cable 200 may be used in, for example, a fiber amplifier (e.g., an EDFA).

[0018] FIG. 2B shows a diagram of a second embodiment a fiber ribbon cable 210 arranged in a pattern of a circular array. The fiber ribbon cable 210 is similar to the fiber ribbon cable 200 described above, however, it has been modified to include three ribbon tubes 105 that contain the heating element 110. Additionally, the ribbon tube in the center position contains the optical fiber 115.

[0019] FIG. 2C shows a diagram of a third embodiment a fiber ribbon cable 220 arranged in a pattern of a circular array. The fiber ribbon cable 220 is similar to the fiber ribbon cable 200 described above, however, it has been modified to include six different optical fibers, optical fiber 115, optical fiber 122, optical fiber 125, optical fiber 130, optical fiber 135, and optical fiber 140. One or more of the six different optical fibers may each transport different optical signals from each other.

[0020] FIG. 2D shows a diagram of a fourth embodiment a fiber ribbon cable 230 arranged in a pattern of a circular array. The fiber ribbon cable 230 is similar to the fiber ribbon cable 210 described above, however, it has been modified to include four different optical fibers, optical fiber 115, optical fiber 122, optical fiber 125, and optical fiber 130. One or more of the four different optical fibers may each transport different optical signals from each other.

[0021] FIG. 3 is a diagram of an example fiber amplifier 300. The fiber amplifier 300 includes photodetectors 305, gain controller 307, pump sources 310 and 315, fiber ribbon cables 320 and 325, heat monitoring devices 330, temperature controller 335, and flattening filter 340.

[0022] The strength of an optical signal input into the fiber amplifier 300 is measured using a photodetector 305. Additionally, the strength of an output signal generated by the fiber amplifier 300 is measured using another photodetector 305. The output from

photodetectors 305 is transmitted to the gain controller 307.

[0023] The gain controller 307 controls the level of gain of the fiber amplifiers based on the output from the photodetectors 305. For example, if the output from the photodetectors 305 indicate that the gain of the optical input signal needs to be increased by 3 dB, the gain controller 307 may adjust one or both of pump sources 310 and 315 to increase the power of the output optical signal.

[0024] The pump sources 310 and 315 produce optical pump output signals that are used to excite ions within the fibers contained in fiber ribbon cables 320 and 325 into higher energy levels. The excited ions can decay via stimulated emission of a photon at the wavelength of the optical input signal back to a lower energy level. The wavelength of a pump output signal is matched to a specific excitation band. For example, if the fiber ribbon cables 320 and 325 are composed of Erbium doped silica, common wavelengths of the pump output signals are 980 nm or 1480 nm. Pump sources 310 and 315 may be for example, a semiconductor laser tuned to a pumping wavelength, or some other light source that produces light at the pumping wavelength.

[0025] In this embodiment, the fiber ribbon cables 320 and 325 may be, for example, fiber ribbon cable 100, fiber ribbon cable 200, fiber ribbon cable 210, or some combination thereof. The fiber ribbon cables 320 and 325 may contain optical fibers doped with Erbium, Ytterbium, or other materials used for creating fiber amplifiers. Additionally, the fiber ribbon cables 320 and 325 may contain one or more heating elements 110. The heating elements 110 are controlled by the temperature controller 335.

[0026] Temperature controller 335 controls the temperature of one or more heating elements contained within fiber ribbon cables 320 and 325. The temperature controller 335 is coupled to heat monitoring devices 330 to monitor the temperature (i.e. fiber temperature) of the optical fibers contained in the ribbon cables 320 and 325. The heat monitoring devices 330, may be for example, thermocouples or some other device used to measure temperature. The temperature controller 335 activates the one or more heating elements 110 when the temperature of the optical fibers contained within the fiber ribbon cables 320 and 325 is less than a specific temperature value (e.g., 60 degrees Celsius). Once the temperature of the optical fibers equals the specific temperature value the temperature controller adjusts or turns off one or more of the heating elements 110 within the optical fibers to maintain the fiber temperature at the specific temperature value.

[0027] Additionally, in some embodiments, the fiber amplifier 300 includes a flattening filter 340. For example, the optical signal amplified by fiber ribbon cable 320 may have wavelength-dependent gain, causing some wavelengths to be amplified more than others. The flattening filter 340 restores all wavelengths to approximately the same intensity.

[0028] Additional Embodiments

[0029] Reconfigurable optical add-drop multiplexer (ROADM) nodes may be used to add/drop optical signals in an optical multi-channel system. The switching points are known as add/drop points. For example, a multi-channel optical signal may contain signals A, B, and C where the signals are intended for different destinations. At the add/drop point signal B may be removed from the original multi-channel optical signal and rerouted to its intended destination.

[0030] Often when such a switching occurs the re-routed channel needs to be amplified. In this embodiment a single fiber amplifier system at the add/drop point may be used to boost the re -rerouted optical signal. The fiber amplifier 300 may be modified to include multiple optical input signals. For example, the gain controller 307 may be configured to monitor a photodetector 305 for each optical fiber containing an optical input signal and for each optical fiber containing an optical output signal. Additionally, the multiple optical fibers containing optical input signals may be coupled into a single fiber ribbon cable, such that a plurality of ribbon tubes within the fiber ribbon cables 320 and 325 contain optical fibers that each carry different optical signals. In this embodiment, fiber ribbon cables 320 and 325 may be, for example, as described above with respect to FIGs IB, 2C, and/or 2D. For example, if the fiber ribbon cable was in a pattern of a linear array as described in FIG. 2B, the optical signals A and C may be carried in the optical fiber 1 15 and the re-routed optical signal B may be carried in the optical fiber 122. Accordingly, a single heating element 110 may be used to maintain the temperature of the optical fiber containing optical signals A and C, as well as the optical fiber containing optical signal B.

[0031] Although the detailed description contains many specifics, these should not be construed as limiting the scope of the disclosure but merely as illustrating different examples and aspects of the disclosure. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

[0032] In the claims, reference to an element in the singular is not intended to mean "one and only one" unless explicitly stated, but rather is meant to mean "one or more." In addition, it is not necessary for a device or method to address every problem that is solvable by different embodiments of the invention in order to be encompassed by the claims.

[0033] Each controller (e.g., temperature controller 335 and gain controller 307) may be implemented in computer hardware, firmware, software, and/or combinations thereof. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits) and other forms of hardware. Some of the methods performed by the computer may be implemented using computer-readable instructions that can be stored on a tangible non-transitory computer-readable medium, such as a semiconductor memory.

Claims

What is claimed is:

1. A fiber ribbon cable comprising:

a plurality of ribbon tubes arranged in a pattern, wherein one of the ribbon tubes contains an optical fiber and an adjacent ribbon tube contains an electric heating element such that when heated the electric heating element is able to adjust the temperature of the optical fiber.

2. The fiber ribbon cable of claim 1, wherein the pattern is a linear array that alternates between a ribbon tube containing an optical fiber and a ribbon tube containing the heating element.

3. The fiber ribbon cable of claim 2, wherein the ribbon tubes containing optical fibers all contain the same optical fiber.

4. The fiber ribbon cable of claim 2, wherein one of the ribbon tubes contains a different optical fiber from the optical fiber.

5. The fiber ribbon cable of claim 1, wherein the pattern is a circular array such that the ribbon tubes are arranged around a ribbon tube in a center position.

6. The fiber ribbon cable of claim 5, wherein the ribbon tube in the center position includes the electric heating element.

7. The fiber ribbon cable of claim 6, wherein a ribbon tube in the circular array includes a different optical fiber.

8. The fiber ribbon cable of claim 5, wherein the electric heating element is included in two or more ribbon tubes and the ribbon tube including the optical fiber is located at the center position.

9. The fiber ribbon cable of claim 8, wherein a ribbon tube in the circular array includes a different optical fiber.

10. The fiber ribbon cable of claim 1, wherein the optical fiber is made out of Erbium doped silica.

11. The fiber ribbon cable of claim 10, wherein the fiber ribbon cable acts as the gain element in an Erbium doped fiber amplifier.